how to initialize a char matrix matrix with empty elements?

swedenguy · #1 22-Aug-2006, 03:41

hello guys!
i have a problem (don't know why) and need some help
I have a matrix se part of the code below

CPP / C++ / C Code:

int i, j;
	char matrix[3][3];
	for(i=0;i<=9; i++) {
		if(bo->square[i].piece_type==1) /*bo->square[i].piece_type return an integer */
			  matrix[i/3][i%3]='+';
		else if (bo->square[i].piece_type==2) /
			matrix[i/3][i%3]='*';
		else matrix[i/3][i%3]=' ';
		}

but i get a run time error when i have the last statement matrix[i/3][i%3]=' ';
If a remove this statement everything is correct but i get some strange (random character) at the empty matrix element when i print it on the screen
Can somebody tell me how do i intialize an element of the matrix with an empty character ' ' without geting this error ?

davekw7x · #2 22-Aug-2006, 10:17

Quote:

Originally Posted by swedenguy

hello guys!
i have a problem (don't know why)

One way to figure it out is to look at the code How many elements are there in the array? How many times does it go through the loop? (A run time error when you are assigning an value to an array element may be an indication that you are going beyond the limits of the array.)

If you can't see it, then make the program tell you what it is working on:

CPP / C++ / C Code:

    for (i = 0; i <= 9; i++) {
        printf("i / 3 = %d, i %% 3 = %d\n", i/3, i%3);
    .
    .
    .
    }

Sometimes I just break out the problem area into a separate small program to make sure nothing else is screwing up the works:

CPP / C++ / C Code:

#include <stdio.h>

int main()
{
    int i;
    char matrix[3][3];

    for (i = 0; i <= 9; i++) {
        printf("i / 3 = %d, i %% 3 = %d\n", i/3, i%3);
        /*matrix[i / 3][i % 3] = ' '; */
    }
    return 0;
}

Or, you could simply use the matrix in a more "natural" way: Instead of trying to calculate index values, you could use nested loops:

CPP / C++ / C Code:

    int i, j;
    char matrix[3][3];

    for (i = 0; i < 3; i++) {
        for (j = 0; j < 3; j++) {
            printf("i = %d, j = %d\n", i, j);
            matrix[i][j] = ' ';
        }
    }

Regards,

Dave

swedenguy · #3 22-Aug-2006, 10:27

Quote:

Originally Posted by davekw7x

One way to figure it out is to look at the code How many elements are there in the array? How many times does it go through the loop? (A run time error when you are assigning an value to an array element may be an indication that you are going beyond the limits of the array.)

If you can't see it, then make the program tell you what it is working on:

CPP / C++ / C Code:

    for (i = 0; i <= 9; i++) {
        printf("i / 3 = %d, i %% 3 = %d\n", i/3, i%3);
    .
    .
    .
    }

Sometimes I just break out the problem area into a separate small program to make sure nothing else is screwing up the works:

CPP / C++ / C Code:

#include <stdio.h>

int main()
{
    int i;
    char matrix[3][3];

    for (i = 0; i <= 9; i++) {
        printf("i / 3 = %d, i %% 3 = %d\n", i/3, i%3);
        /*matrix[i / 3][i % 3] = ' '; */
    }
    return 0;
}

Or, you could simply use the matrix in a more "natural" way: Instead of trying to calculate index values, you could use nested loops:

CPP / C++ / C Code:

    int i, j;
    char matrix[3][3];

    for (i = 0; i < 3; i++) {
        for (j = 0; j < 3; j++) {
            printf("i = %d, j = %d\n", i, j);
            matrix[i][j] = ' ';
        }
    }

Regards,

Dave

yes you are right Dave. Thank you for sharing your experience/knowledge with you. The error was as "ususal" uín this case when going beyond the array in my case for (i = 0; i <= 9; i++) should be for (i = 0; i < 9; i++)

WaltP · #4 22-Aug-2006, 11:37

Please do not double post. I wasted time answering your other post. One post is enough.

davekw7x · #5 22-Aug-2006, 11:43

Quote:

Originally Posted by swedenguy

yes you are right Dave. Thank you for sharing your experience/knowledge with you. The error was as "ususal" uín this case when going beyond the array in my case for (i = 0; i <= 9; i++) should be for (i = 0; i < 9; i++)

Yes, that works.

However...

Why not just use the nested loops. That way there's not much question about what it is doing (I suggest that it's likely to be more efficient in terms of machine code and time as well as debugging time.)

Regards,

Dave

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how to initialize a char matrix matrix with empty elements?

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